Tire Size Calculator
Calculate tire dimensions from a size code like 225/55R17. Get sidewall height, overall diameter, circumference, and compare two tire sizes for speedometer accuracy.
Format: Width/AspectRatioR{rimDiameter}
About the Tire Size Calculator
Tire size codes like "225/55R17" encode three measurements: section width in millimeters (225), aspect ratio as a percentage of section width (55%), and rim diameter in inches (17). The sidewall height = 225 × 0.55 = 123.75 mm. Overall diameter = 17 × 25.4 + 2 × 123.75 = 679.3 mm. When switching tire sizes, speedometer accuracy depends on maintaining similar circumference. For unit conversions between mm and inches, use our Unit Conversion Calculator.
A speedometer error over ±3% can affect odometer readings and potentially trigger speeding fines. The comparison mode helps you evaluate whether a plus-sizing upgrade (wider tires on a larger rim) maintains legal and practical accuracy. For more automotive calculations, check our Area Calculator for contact patch estimates.
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For a related calculation, use Mass Calculator to convert between all mass units: mg, g, kg, metric ton, oz, lb, stone, short ton, and long ton. Alternatively, use Shoe Size Conversion to convert shoe sizes between US, UK, EU, and CM foot length for men's and women's footwear.
For the underlying method, read Unit Conversion Guide: Metric, Imperial, and the Math That Connects Them.